Fried Clutches

[Pittenger5]

So word has it that 2 racers friend clutches at Daytona, so how sensitive are these stupid things? I always kind of thought a fried clutch was an excuse a lot of people use, and I cant imagine factory bikes dont change these things ever. So my assumption is these guys fried their clutch in a relatively short amount of time, how does this happen? And what are the symptoms when it DOES happen?

[BLACK SQUIRREL]

On the Launch is where it happens

[Tabby]

I'm curious about that too. I've beat the living hell out of my clutches at the drags, and have never had one just plain give up, on the spot. I'd get about 20,000miles minimum out of an OEM. Maybe at the power levels those fellows are working at, the clutch gets much less forgiving, or maybe they haven't spent any time at the drags themselves, to learn how to launch with out frying one. Enquiring minds want to know.

Symptoms? It slips! If the clutch doesn't fail outright, the slippage will occur when you put a heavy load on it. Depends how bad it got cooked. Say you are trying to get a good drive out of a corner, so you might be grunting it a bit. You will hear and feel the revs not match the drive, or you will hear and feel the same thing when the engine really starts to climb up on the cam.

[BMFR6]

symptoms: hold front brake, give it some gas and start letting the clutch out. if your wheel doesn't start to spin, your clutch is either fubar or poorly adjusted. you'll smell it when you do fry one.

[Pittenger5]

On the Launch is where it happens

So, then my question is, how sensitive are they? I understand top pros use their equipment harder than "normal" guys, but I would think they're smoother on the clutch than a club racer, so how come theirs go?

symptoms:

So if one goes, youre just not putting power to the wheel? Or is your engine braking affected? Is the clutch considered engaged when youre pulling the lever, or not pulling the lever? I need to learn how this shit works someday.

[Tabby]

It can feel a bit like spinning the rear tire on wet pavement,,,, without the slideways antics. Just because the pros are as fast as they are, if they haven't done any real drag racing, their launch skills might not be any better than your average club racer.
Just go to the drags and find out for yourself. It isn't a big deal. Also, clutches tend to be cheaper than a rear tire, and quite a bit easier to change.

[BMFR6]

So, then my question is, how sensitive are they? I understand top pros use their equipment harder than "normal" guys, but I would think they're smoother on the clutch than a club racer, so how come theirs go?



So if one goes, youre just not putting power to the wheel? Or is your engine braking affected? Is the clutch considered engaged when youre pulling the lever, or not pulling the lever? I need to learn how this shit works someday.

I'm not too sure about the AMA guys, but at the GP level their clutches are built for 2 maybe 3 launches at best which is why you see riders have issues on the start if a race is red flagged. I don't know the real reasonig as to why they are built that way though. The clutch is probably seen as a weak point in the drive train.

You're correct, if it's gone you aren't getting anything to the wheel. On track you would notice as you roll on out of a corner, the rpm's build but you're not really going anywhere. The clutch is "engaged" when you are "not" pulling on the lever; all those plates are squished or clutched together. When you pull the lever, it disengages and the plates seperate allowing the engine to spin with out transferring the power to the wheel. Pull one aprt some time, you'll figure it out pretty quick.

[Pittenger5]

their clutches are built for 2 maybe 3 launches at best

Well the rest of that makes sense relatively. I cant imagine why they would have it designed like this though. I would think its one more thing to go wrong, without a whole lot of benefit, but Im sure theres a reason there somewhere.

[Paul_E_D]

I'm sure a lot of guys aren't using stock clutches, and then some guys are never maintaining their clutches. Also, adding power to a bike can quickly smoke a stock clutch as it's designed to work in a certain power range. Often the springs will be too weak for the added power.

Sometimes you overheat the steel plates on a start and they warp. The whole clutch isn't bad, just the warped plate. Replace it and play again.

Many guys will run aluminum plates for weight reduction. These can wear fast and or crack.

So there's a lot of factors. Stock bike, stock clutch and things usually last a while.

When a clutch fails, it starts slipping under power in heavy load situations. Going up the hill into T5 at Loudon, or on the banking at Daytona. You won't feel it failing under engine braking because that's not heavy load. When they fail, they tend to go quickly as all that slipping warps disks and then, boom, no clutch at all.

[Paul_E_D]

p.s., It's the tall gearing on a GP bike that eats clutches. They don't need first gear for around town, so it's similar to 3rd gear on a street bike. This requires huge revs to get it going and heats the clutches big time.

[Pittenger5]

Often the springs will be too weak for the added power.

Elaborate? How does a stiffer or softer spring affect power? From what I understand a stiffer spring helps improve the clutches longevity, but I may be wrong there.

[BMFR6]

ah, that makes sense. i knew about the gearing but didn't put two and two together. thanks.

[obsolete]

Elaborate? How does a stiffer or softer spring affect power? From what I understand a stiffer spring helps improve the clutches longevity, but I may be wrong there.

If the bike makes more power you will probably need stronger springs to overcome the added power of the engine trying to slip the clutch.

[Tabby]

p.s., It's the tall gearing on a GP bike that eats clutches. They don't need first gear for around town, so it's similar to 3rd gear on a street bike. This requires huge revs to get it going and heats the clutches big time.

Forgot about the tall gearing. That certainly doesn't make it any easier.
For a given size clutch, stiffer springs do help longevity. You can play with the friction material also. It does come down to how much grip force or friction that can be maintained. With an existing clutch, you don't have many options to improve what is there. In some cases, an extra drive and driven plate can be squeezed into the existing basket, but boy oh boy, does that make the initial "take up" really fussy.

[Paul_E_D]

When you release the clutch, the springs push the friction plates against the steels, like a brake caliper squeezing pads. The stock spring push hard enough to hold against slipping for the stock HP output. Add HP and the springs aren't pushing hard enough under really high load situations like starts. More slippage happens, generating more heat and more wear.

[Pittenger5]

Ahh alright, makes sense, thanks.

[NeverlosT]

im not sure if your question was specific to racing (so my comments here wont apply), but I friend the clutch on my 2007 VFR800 being a moron on a trip to canada. Was clutching up wheelies on an abandoned interstate and after one last go at it I realized "hey, I cant shift down anymore". I could shift up though. I got myself stuck in 6th gear and cruised to the next town and the bike died on the offramp. The clutch plates were shredded and welded together.

It was taken care of by warranty THAT night at a dealership and ready the next morning. SWEET! They actually said my foolishness had helped, but not caused the problem. I still didnt feel better about busting up my VFR though...

in my case, it didnt smell, it just didnt shift anymore. The clutch lever didnt actuate anything anymore.

[CBR929RE]

im not sure if your question was specific to racing (so my comments here wont apply), but I friend the clutch on my 2007 VFR800 being a moron on a trip to canada. Was clutching up wheelies on an abandoned interstate and after one last go at it I realized "hey, I cant shift down anymore". I could shift up though. I got myself stuck in 6th gear and cruised to the next town and the bike died on the offramp. The clutch plates were shredded and welded together.

It was taken care of by warranty THAT night at a dealership and ready the next morning. SWEET! They actually said my foolishness had helped, but not caused the problem. I still didnt feel better about busting up my VFR though...

in my case, it didnt smell, it just didnt shift anymore. The clutch lever didnt actuate anything anymore.

if you couldn't shift then there was another issue. but clutching up a 550lb bike certainly isn't gonna help anything.

[13]

I killed the clutch in my 600 my first season by practicing launches a few times a weekend. It started feeling like a snowmobile coming onto the front straight. Last season I didn't practice starts as often, and it's still good.

[scottieducati]

I doubt drag bikes use slipper clutches. Slippers (generally) have much reduced life-spans versus OEM or non-slipper aftermarket. Larry Pegram on his FX 848 (150HP, not even a super bike) had a custom clutch cover installed so they could access the clutch quickly, he needed a new one after *every* start. So red flag.... means they had to replace it before the restart.

[BLACK SQUIRREL]

I doubt drag bikes use slipper clutches. Slippers (generally) have much reduced life-spans versus OEM or non-slipper aftermarket. Larry Pegram on his FX 848 (150HP, not even a super bike) had a custom clutch cover installed so they could access the clutch quickly, he needed a new one after *every* start. So red flag.... means they had to replace it before the restart.

Do you mean his 749 I think Formula extreme Predates the 848. by a year

[CBR929RE]

Do you mean his 749 I think Formula extreme Predates the 848. by a year

he ran a Bucci slipper in the 749/848 FX bikes. a friend of mine once had his backup one.